1. Field of the Invention
The invention relates to a vehicular projector headlamp that employs a plurality of LED elements as light sources and that emits a sufficient luminous flux.
2. Description of the Related Art
Japanese Patent Application Publication No. 2003-317513 (JP-A-2003-317513) describes a light source unit of a vehicular lamp. The light source unit employs an LED element as a light source. The light source unit includes a reflector. The reflector has a first focal point and a second focal point. The first focal point is located at the LED element that serves as the light source. The second focal point is located at a rear focal point of a projection lens. Light emitted from the LED element is reflected by the reflector toward a region proximate to the rear focal point of the projection lens. Part of the reflected light is blocked by a light control member (shade) located in proximity to the focal point to become diffused light, and exits forward of the projection lens.
Japanese Patent Application Publication No. 2005-108554 (JP-A-2005-108554) describes a vehicular headlamp that uses two semiconductor light-emitting elements as light sources. In the vehicular headlamp, the first and second semiconductor light-emitting elements are arranged on opposite sides of a forward travel blocking member (shade). Rays of light from the two light sources are respectively reflected by first and second reflectors toward a region proximate to a rear focal point of a projection lens. Then, light passing through the distal end of the forward travel blocking member becomes diffused light, and exits forward of the projection lens.
An LED element, for example, has advantages in that the luminous efficacy is high and the service life is long as compared with a filament bulb; however, it is difficult for a luminous flux of light emitted from the LED element to be diffused. In addition, in the light source unit described in JP-A-2003-317513, light emitted from the single LED element is reflected by the reflector to diffuse the luminous flux; however, the diffusion is insufficient to cause poor light distribution. Thus, in a vehicular headlamp that uses an LED element as a light source, as shown in FIG. 5, a plurality of light source units 21, which correspond to the above described light source unit, are provided in a lamp unit 24 arranged inside a lamp chamber S1 formed inside of a front cover 22 and a lamp body 23. In so doing, the luminous flux is increased to thereby enhance light distribution.
However, the flexibility of arrangement of the light source units 21 in the lamp chamber S1 is limited. Thus, when the plurality of light source units 21 are arranged, part of luminous flux (indicated by the broken line A in the drawing) of light emitted from an LED element 26 and reflected by a reflector 25 is blocked by a mounting portion 27 of the adjacent LED element as shown in FIG. 5. Therefore, there is a large loss of light flux, resulting in a decrease in a luminous flux condensed to a region proximate to the rear focal point of the projection lens.
Moreover, an LED element that emits a large amount of light is employed as a vehicular headlamp. Therefore, the LED element has a heating value higher than that of a general LED element. Thus, as described in JP-A-2005-108554, when the two semiconductor light-emitting elements are arranged on opposite sides of the shade, the radiation amount of heat generated by the two LED elements is small, and those LED elements are heated by the generated heat. This may decrease the intensity of luminous flux of the emitted light.